1. Field of the Invention
The present invention relates to a seal structure for sealing two members in a fluid-tight or an air-tight manner by a seal portion formed by printing.
2. Prior Art
Generally, a seal structure for sealing two members by holding a gasket made of a synthetic rubber, metal, or paper between the two members has been employed as a seal structure for sealing between two members in a fluid-tight or air-tight manner.
However, when the above type of seal structure is employed to, for example, a control valve unit of an automatic transmission for an automotive vehicle, a plurality of gaskets are necessary so that the operability of assembling the unit is deteriorated. Further, it is necessary to form a multiplicity of through holes on the gasket in correspondence to an oil passage, so that there are problems in that a cost for manufacturing the gasket is increased and that the design of unit cannot be easily changed.
Then, a seal structure manufactured in a low cost and having an excellent operability of assembling has been suggested by printing a synthetic rubber material to one of joint surfaces between two members along a seal portion by a screen printing so as to integrally form the seal portion.
In this kind of seal structure, basically when the width of the seal portion is increased, the height of the seal portion is slightly increased due to the fact that a surface tension of the material and a contact area against the joint surface becomes large so as to reduce a surface pressure, thereby being difficult to compress, and when the width of the seal portion is decreased, the height of the seal portion is slightly reduced due to the fact that a surface tension of the material and a contact area against the joint surface becomes small so as to increase a surface pressure, thereby being easy compress.
Accordingly, in order to improve a total sealing performance, it is preferable to reduce the width of the sealing portion. However, when the width is reduced much, the contact area of the seal portion becomes small and a problem of break away is generated. Therefore, the seal portion is normally narrowed to a degree such that the break away is not generated, thereby securing a proper sealing performance.
On the other hand, in order to improve a sealing performance locally, it is structured that the width of the seal portion is increased and the height of the seal portion is increased, thereby increasing a sealing performance. Further, at a portion in which a surface pressure is increased near a fastened portion by a bolt, it is structured that the width of the seal portion is reduced so as to reduce the height of the seal portion and a compression deformation is easily occurred, so that the other sealing portion is prevented from deteriorating a sealing performance.
In the above seal structure, since the width of the seal portion is increased at a meeting portion in which a plurality of seal portions are crossed together so as to increase the height of the seal portion, there is a problem that a sealing performance near the meeting portion is deteriorated.
Further, although it is possible to locally improve the seal performance by increasing the width of the seal portion in the above manner, often this structure cannot be applied to an apparatus such as a control valve which is greatly limited in the width of the seal portion.
Still further, in the case that the width of the seal portion is reduced and the compression deformation is easily performed so as to prevent a local surface pressure near the fastened portion by a bolt, since it is necessary to relatively reduce the width of the seal portion in the local portion by increasing the width of the seal portion of the other portion so as to solve the break away of the seal portion, the structure cannot be often applied to the apparatus such as a control valve in the same manner as to the above.
Furthermore, in the case of locally adjusting the width of the seal portion in the above manner, since the seal height of the local portion becomes high and the sealing performance near the portion is changed, in the event, a total design change is necessary so that the design and the design change of the seal portion become complicated.